Safety Warnings
This demonstration uses 50 V at 15 A (750 W). Ensure all connections are secure before powering on. Use insulated ceramic insulators to prevent electrical contact with metal stands. Keep the variac off until ready to demonstrate, and never touch the wire or connections while powered.
The wire reaches temperatures exceeding 900°C during operation. The wire will glow red-hot and can cause severe burns or ignite nearby materials. Maintain a clear zone of at least 0.5 m around the wire. Do not allow the heated wire to contact the Styrofoam ball for extended periods as it will melt or ignite. Keep fire extinguisher accessible.
Excessive current or prolonged heating may cause the wire to melt and break. If the wire breaks, it may fall or swing unpredictably. Do not exceed 15 A current and limit demonstration time to 30-60 seconds. Allow the wire to cool completely between repeated demonstrations.
Purpose
Demonstrates thermal expansion and a solid-solid phase transition in iron. A current-heated wire sags as it expands, then visibly contracts when iron transforms from BCC (α-iron) to FCC (γ-iron) at ~912°C, before continuing to expand. Shows that phase transitions are not limited to solid-liquid-gas changes.
